Editor's note: CNN's Nick Paton Walsh returned to the Syrian city of Aleppo recently where he saw severe devastation wrought by the ongoing civil war.

Aleppo, Syria (CNN) - The smell of burnt plastic leaps out at you. Acrid in the throat, omnipresent, extinguishing from the air all the other smells of city life - because really there is none. The scenes of destruction - the fact every street is pockmarked by two years of shelling - you have seen in activist videos online. But the smell is something striking: it notifies you that you are on the edge of humanity.

Donetsk, Ukraine (CNN) – A battle between pro-Russia separatists and government forces at Donetsk airport in eastern Ukraine has claimed 40 lives, authorities said Tuesday, in what is the deadliest outbreak of violence yet in the flashpoint city.

An additional 31 people have been injured, including four civilians, according to the website of the Donetsk mayor, Alexander Lukyanchenko. Two of the fatalities are civilians.

Slovyansk, Ukraine (CNN) - Russian Foreign Minister Sergey Lavrov on Tuesday ruled out holding a second international meeting in a bid to defuse the crisis in Ukraine, also saying it would be "unusual" to hold a presidential election in the country when the army was being deployed against the population.

In what could be a sign of Moscow preparing to question the legitimacy of the May 25 presidential election if it is unhappy with the process, Lavrov said, "In the situation where they use the army against their own population, it's quite unusual."

(CNN) - Ukrainian security forces battled pro-Russian militants in the eastern flashpoint city of Slovyansk on Monday as Kiev tackled the gunmen who have overrun the region.

Military gains were evident on the main highway into Slovyansk, a rebel stronghold, as government forces moved in.

A CNN team on the ground saw a substantial number of militants bolster their defensive positions and checkpoints inside the city. One civilian car was hit in the fighting, its exterior damaged by bullet holes.

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